Power assist manufacturers are supplying consumers with power-assist drives that power bicycles. These power-assist systems drive either the front or rear tire enabling forward movement. Such systems provide a viable alternative to pedaling and add an enjoyment to riding. Most systems on the market today consist of either friction or direct drive systems.
Friction drive systems, like U.S. Pat. No. 5,491,390 to McGreen (1996), comprise the majority of what is on the market today. Friction drive systems consist of electric motors that are connected to rollers or belts that contact the tire patch. These systems are mounted on the bicycle frame for use on either the front or rear tire. The rollers or belts are manually or automatically clamped down onto the tire when power is applied. When the electric motors are on and turning, the frictional contact between the tire and the roller or belt causes the wheel of the bicycle to turn in unison. The drawbacks to these systems are:
(a) increased wear and tear of the tire when used as a driving surface, PA1 (b) traction is lost when the tire gets wet, PA1 (c) tires need to have smooth surfaces to maximize contact to the roller or drive belt, PA1 (d) road dirt and grime collects on the roller or belt when contacting tire. PA1 (a) to provide a drive eliminating tire slip inherent in frictional roller drives. PA1 (b) to provide a drive comparable to gear driven systems that places its components within the centerline of the bicycle. PA1 (c) to provide a drive comparable to hub driven systems, but without the high cost of custom internal gear designs. PA1 (d) to provide a freedom to choose different tire combinations for varying terrain, unlike the specific tires needed in frictional driven systems. PA1 (e) to provide an ability to easily change drive ratios to meet each and everyone's personal needs. PA1 (f) to provide a design that uses off-the-shelf components that can be readily replaced or modified without relying on the manufacturer for customized parts.
All these problems would be eliminated if we went to direct drive systems that use a system of gears or hub motors to drive the rim of the wheel instead of the tire patch.
Like friction drive systems, gear drive systems are implemented on either the front or rear tire of a bicycle. Gear drive systems comprise of an electric motor mounted to the bicycle frame with a chain or belt affixed to a gear on the motor shaft and a gear on the tire rim. When power is applied, the motor turns the wheel. Many gear systems require installing long chains or belts that can snag or get caught on something during operation. Some of these systems are single stage systems that require very small gears at the motor shaft and very large gears attached to the rim in order to achieve a ratio comparable to turn the wheel. Still other systems require pedaling before the motor will start to spin. Other systems, like U.S. Pat. No. 5,937,964 to Mayer et al. (1999), mount on the side of the rear wheel that leave its components protruding pass the bicycle's centerline increasing the possibility for tremendous damage when an obstruction gets tangled during forward movement.
Hub motor drives are another type of direct drive system. An electric motor is either confined within the hub or it is the hub of the wheel itself. This hub rides on its axis and is connected to the rim and tire via spokes. When power is applied to the hub motor, the whole wheel turns in reference to the hub axis that supports the entire wheel. Hub drive systems can be used on either the front or rear wheel of a bicycle. The biggest drawback to a hub system is cost. Hub motors need to be custom designed to fit within the confines of a wheel within a bicycle frame. Because of this confinement, the choice of motors are limited to smaller and less powerful motors that will degrade performance trying to keep costs reasonable. Most hub drives are custom designs and are not derived from off-the-shelf components. These designs are fixed and not easily modified for different terrain.
All of these inventions assist bicyclists on their rides. They provide viable alternatives to pedaling. However, we need a system that is a better alternative to current frictional and direct drive systems that use off-the-shelf parts and will give the user an ability to easily customize the assist system to their personal tastes and terrain.